Basically, strictly within the networking concept itself, you can have trunk interfaces (tagged ports) and access ports (untagged ports).
When you specify a tag of X, vlan X is created. What dictates further the choice of tagged vs untagged is the device and configuration at the other end of the link.
So you could then have two cases:
a) The port is tagged - meaning, it is a trunk port. Furthermore, it accepts incoming tagged frames and tags frames before sending them out. You setup a trunk port if your F5 connects to another trunk port - normally on another switch. In this configuration you are basically aggregating traffic from all vlans, on a single port.
b) The ports is untagged - in this case, you are configuring an access port in vlan X - simple as that. You could have more than one port in the same VLAN - think of it as a switch with more than one port in the same vlan ... so hosts connected to those two ports can communicate directly as they will be in the same broadcast domain. Unlike with trunk ports, here you are segregating the traffic into multiple vlans.